[Tami]

Hi,

I'm afraid, that this is a very basic question, still I couldn't find a clear explanation anywhere. I need to know what a statement like "On average x% of substance y will be absorbed after ingestion" really means, especially if it's a substance that's not easily soluble.

For example, let's take elemental lead. I've read something like "Children will absorb 50% of ingested lead.". But if a child swallows a small solid piece of lead, it will pass through and certainly not loose half it's mass. So what do those 50% mean? Does it mean that 50% of the lead which was solved in the stomach acid is absorbed?

Thanks in advance!

[Arkcon]

Pretty much that yes.  For a particular form of lead, X% will be absorbed by the body by whatever route in question.  They will quote different percentages for various compounds, and physical forums, say large lumps vs powders, or if another component helps it along, or various routes, say through the skin or injected, instead of swallowed.  FWIW, lumps of elemental lead, or mercury as another example, are not well absorbed by the human G.I. tract.  (Not that people should go around eating those.)  However, certain soluble salts, especially organic salts, are very toxic by ingestion.  Even worse by inhalation.

[Tami]

But for elemental lead you always find this 10% number for adults and 50% for children, it's never said to what physical form this refers (large lumps vs. fine particles), only that it must be elemental lead (as you said the given absorption rate for lead salts is much higher, more than 90% for adults).

[Arkcon]

Does it really say that they specifically mean metallic lead?  Or do they just mean the general environmental sources of lead, typically lead oxide used in old paints?

[Tami]

... it's often phrased a bit confusing (like in the Wikipedia article "Lead poisoning"). But I think you're right, this article makes it clear that inorganic lead compounds in general are meant:

Inorganic lead salts enter the body by way of ingestion or inhalation. For adults, only about 10% of the ingested dose is absorbed. In contrast, children may absorb as much as 50% of an ingested dose.

  So, inorganic salts are not so dangerous... What about "lead sugar" (Lead(II) acetate) is that classified as organic salt?

And if one swallows pure metallic lead, what would be the chemical reaction? Is lead chloride produced?

[Arkcon]

Yes, I would expect metallic lead to become lead chloride, an insoluble salt, when it hits stomach acid.  I wouldn't guarantee its not dangerous, in fact swallowing a fishing lure can definitely increase serum levels of lead. http://en.wikipedia.org/wiki/Lead_poisoning#Lead-containing_products  Even inorganic salts can be absorbed, what really matters is exposure level -- water or soil contamination where a person lives, or exposure to household contaminates.  And yes, lead acetate is definitely one of the organic salts of lead, although I don't know how common it is, outside of Ancient Rome.

[Arkcon]

I don't really understand what the authors mean with the statistic you keep quoting, that adults absorbed 10% while children absorb 50%.  Lead poisoning in adults has serious symptoms, but in children it can cause permanent damage to developing nerves.  And children are smaller, so smaller amount have greater effect.  And maybe because children grow rapidly, they may have greater absorption.  But I think this quoted factoid is just an artifact based on a combination of all those effects.

[Tami]

Ok, thanks.
Regarding lead sugar, yes, I read that the Romans used it as sweetener, especially for wine... honestly, I find it nearly unbelievable, that they didn't notice it's toxic effect.

[Arkcon]

Numerous natural historians of the time noted a variety of health effects from consumption of sugar of lead.  Its hard to know just how prevalent eating it was.  It may have been a much more rare occurrence than initially thought.